(1) Field of the Invention
The present invention relates to a method for manufacturing a printed circuit board, and more particularly to a method for manufacturing a printed circuit board having electrodes on an end face of a substrate.
(2) Description of the Related Art
As a conventional method for manufacturing a printed circuit board, a technology well known (hereinafter referred to as a first prior art) is one in which a substrate having through-holes formed therein is cut at a plane passing through the through-holes by means of metal press or router cutting processes whereby the end face through-holes are formed with each of the internal portions of the through-holes being exposed in a semi-circular form at an outer end face of the printed circuit board.
Another technology (hereinafter referred to as a second prior art) which is an improvement of the first prior art has been disclosed in Japanese Patent Application Kokai Publication Hei 3-187292. FIGS. 1A and 1B are diagrams for use in explaining the method disclosed in that publication. FIG. 1A is a sectional view taken along a line 1A--1A in FIG. 1B. As shown therein, first, a substrate 5 prepared by a known method is copper plated 6 and resin 8 is filled in a through-hole 7 therein. Then, as seen in FIGS. 2A and 2B (FIG. 2A being a sectional view taken along a line 2A--2A in FIG. 2B), the substrate 5 is cut into two halves in a plane passing through the through-hole 7 by using such means as metal press or router processes. Thereafter, as seen in FIGS. 3A and 3B (FIG. 3A being a sectional view taken along a line 3A-3A in FIG. 8B), the resin 8 present in the end face through-hole 7 is removed using chemicals. According to this method, since the resin 8 exists in the through-hole 7 during the cutting process, it is possible to prevent the plated layer 6 from being damaged or peeled off.
However, the conventional methods for manufacturing the printed circuit board explained above suffer from the problems as follows:
(1) During the cutting process with the first prior art technology where use is made of the metal press, the plated layer on the inner wall of the through-hole is pulled down vertically along the through-hole so that the plated layer develops burrs pointing downward from the bottom of the end face through-hole and also there are possibilities for the land in the direction underneath the press to be damaged and for the plated layer to be peeled off. PA1 (2) Also, during the cutting process with the first prior art technology where use is made of the router process, the plated layer on an inner wall of the through-hole is pulled laterally along the through-hole so that the plated layer develops burrs from the side of the end face through-hole and also there are possibilities for the plated layer to be peeled off from the inner well of the through-hole. PA1 (3) In the method for manufacturing a printed circuit board disclosed in Japanese Patent Application Kokai Publication No. Hei 3-187292, phenomena such as the damaging of or the peeling-off from the through-hole do not occur because the cutting process is carried out with the inside of the through-hole being filled with the resin. However, as seen in FIGS. 2A and 2B, because the end portion of the end face through-hole is subjected to the cutting process, the burrs do develop in the same way as in the first prior art technology. FIG. 4 shows the state in which the burrs 10 develop when the metal press is used for the cutting. PA1 forming a hole at a predetermined position of a laminate board whose two surfaces are copper plated; PA1 filling in the hole with copper paste; PA1 forming a circuit pattern such that a copper foil portion remains only in one half of the hole; and PA1 etching away an exposed region of the substrate. PA1 (1) Because no mechanical process is used in the formation of the end face through-hole, it is possible to obtain the end face through-hole which is free from the development of burrs in or peeling off of a conductive layer. PA1 (2) Because the conductor (formed as a thick conductive layer) formed in a cylindrical shape is present at the end face unlike in the conventional configuration of the through-hole in which the inside of the hole is exposed in a semi-cylindrical shape at the end face of the printed circuit board, it is possible to obtain the side face electrodes in which the reliability is ensured.